It is known in the art to provide for jet ignition of lean mixtures in engine combustion chambers by ignition of rich mixtures in adjacent small ignition chambers connected with the main chambers by restricted orifices. It is further known to supply the main combustion and auxiliary ignition chambers with separately carbureted, or otherwise formed, lean and rich mixtures, respectively, through separate induction passages having their own inlet valves. In general, the arrangement of the dual inlet valves for the main and auxiliary chambers and the mechanism for actuating these valves adds complexity to the design of internal combustion engines, as compared to spark ignition engines that are not provided with separate ignition chambers.